In actual application, there is a requirement, that is, an authorized mission critical push to talk (MCPTT for short) user may temporarily group several MCPTT groups into a temporary group. For example, in some emergencies, a fire department and a public security department work together, and an on-scene commander may need to temporarily group the two MCPTT groups of the fire department and the public security department into a new large group. This MCPTT group regrouping function cannot be supported in the conventional art yet.